One of the Senate's most outspoken proponents of changing the chamber's rules said Wednesday that another handshake compromise is not an option.

"A third 'gentlemen's agreement' is not an acceptable outcome," Sen. Jeff Merkley, D-Ore., said during a joint appearance with AFL-CIO President Richard Trumka Wednesday morning.

Merkley was referring to the results of the two prior efforts to change the Senate's rules to curtail the ability of a minority of senators to filibuster using what's often known as the "nuclear option." In those cases, senators reached bipartisan deals on more narrow changes that have had dubious results.

He said that the level of concern about future repercussions when the roles reverse and a Republican president sends nominees to a GOP-led Senate have been fading.

"It is lessening because the frustration is growing. In other words, a modest amount of obstruction, an occasional request for a supermajority ... once or twice a year might be one thing, but when it's continuous on person after person after person, it's just a very clear strategy to disable an administration re-elected by the American people," Merkley said.

That may also be in part because of the reduced number of Democratic senators with experience serving with a GOP majority leader.

"If anyone thinks a future President Perry or a future President Palin and a future Majority Leader McConnell are not going to work together and if necessary change the rules as they proposed in 2005 to get nominations considered, I think you're probably in an ... imaginary world," Merkley said.

Majority Leader Harry Reid, D-Nev., told reporters Tuesday that he intends to outline a way forward on nominations at a Democratic caucus meeting Thursday. Merkley, who met with Reid about the subject Tuesday, suggested Democrats are prepared to push ahead with a move to eliminate super-majority requirements for confirming presidential nominees to executive departments and agencies.

He said the current focus is on the executive branch, not judges and legislative business.

"I think what you're going to have is a unified caucus coming out of there saying you've proven to us you won't keep your word," Trumka said, in reference to Senate Republicans. "This is about obstructionism, and if you continue to obstruct, we will use the rules to force you not to be able to obstruct."

The labor movement has gotten involved because the National Labor Relations Board is mere weeks away from being unable to secure a quorum to conduct business. President Barack Obama's nominees to the board have yet to face floor votes. Republicans say that at least two of the picks will not get GOP votes to overcome procedural hurdles, citing disputed recess appointments.

"Give these people an up-or-down vote, or we'll make sure that they get an up-or-down vote," Trumka said.

"We're trying to educate as many people as we can. We're educating our members, we're educating our partners, we're educating ... the general public," Trumka said. "We're running a full-fledged campaign on this."

Trumka said he was meeting with senators to encourage support for using any means needed to ensure a fully-functioning NLRB.

On the other side, Minority Leader Mitch McConnell, R-Ky., made another in what's become a regular series of Senate floor speeches arguing against changing the rules with a simple majority, saying presidential nominations have been moving along. He predicted that Reid will set up a sequence of votes on contentious no

“It’s why we see them bringing out all the nominees who’ve been appointed to office illegally, or who are exceedingly controversial," McConnell said. "Democrats themselves have delayed consideration of these nominees for months — that’s Democrats who did that — so they could pull all of them out of the woodwork, all at the same time, in the hopes the Senate would reject them."